We will propose to investigate the role of the phospholipid and Ca2+-dependent protein kinase (protein kinase C) in the maturation of human myeloid leukemia cells. Activation of protein kinase C is the likely mechanism by which the phorbol diesters and conditioned medium from mononuclear cells induce macrophage maturation of human myeloid cell lines and fresh explants of acute and chronic human myeloid leukemia. We will purify the enzyme from human promyelocytic leukemia cells to homogeneity using classical and affinity purification techniques. Physical and kinetic properties of the enzyme will be determined, with particular emphasis on binding of and activation by the phorbol diesters. Defined diacylglycerols will be prepared and their activities as kinase activators, inducers of maturation and ligands for the phorbol diester receptor correlated. Antibodies and organelle fractionation will be used to determine the intracellular distribution of the enzyme. Protein phosphorylation patterns in whole cells and membrane preparations will be determined and correlated with macrophage maturation. The long-term objective of this project is to begin to understand myeloid maturation at a biochemical level. The major scientific disciplines involved are hematology, oncology and cell biology. In vivo maturation of promyelocytic leukemia cells serves as a model for bone marrow differentiation. Studies such as these may define the molecular defect which leads to cessation of myeloid maturation and hence, leukemia. The investigation is health-related because it explores a molecular pathway of differentiation which is blocked in leukemia. Agents active as inducers of cell maturation will soon find clinical application in the experimental treatment of leukemia and other malignancies.